In such structures the earth is stabilised throughout the mass by frictional engagement with the stabilising elements which are usually in the form of strips. This interaction enables the earth mass to behave as an elastic material with greatly improved resistance to failure. The facing of such a stabilised earth structures can be relatively light and has hitherto largely been built up from either V-shaped channel members of 3 mm steel or relatively thin concrete panels which are connected to the forward ends of the stabilising strips. However, even such relatively light panels represent a major element of the cost of the structure and there is a need for stabilised earth structures having a less costly facing.
It has been proposed to retain the earth at the facing of a structure stabilised by layers of embedded mesh by continuing the mesh cover the facing. Thus each element of the mesh which extends rearwardly to stabilise the earth has a corresponding continuation forming part of the facing, which may lead to a rather more substantial facing than required by the earth pressures. Furthermore the stabilising elements of the mesh embedded in the soil tend to separate the mass into layers, giving rise to less uniform stabilisation of the earth than when using strip stabilising elements.
According to one aspect of the invention there is provided an earth structure having a plurality of elongate stabilising elements extending rearwardly from a facing of the structure into an earth mass, the facing comprising at least two laterally spaced support members each connected to a pair of said stabilising elements at lower and upper points of the member, and a mesh cover spanning the lateral space between the support members, the mesh cover having a front portion supported by the support members against forward movement under earth pressure, and at least one substantially horizontal rearwardly projecting portion for stiffening the cover against such forward movement.
The invention also provides a facing panel for such a structure, comprising at least two laterally spaced support members each having means for securing said lower and upper point of the member to said stabilising elements, and a mesh cover spanning the lateral space between the support members, the mesh cover having a front portion supported in use by the support members against forward movement under earth pressure, and at least one substantially horizontal rearwardly projecting portion for stiffening the cover against such forward movement.
The invention also provides a facing for an earth structure, the facing comprising an array of facing panels according to the invention assembled to provide a continuous facing.
With such an arrangement, the support members are located and supported by the elongate stabilising elements embedded in the earth, and the separately provided grid cover may be of relatively lightweight construction designed to accommodate the earth pressures at the facing. Thus the structure may be relatively inexpensive and is particularly useful when the structure is to be temporary or of low height e.g. 3 to 6 meters.
The support members are preferably generally C-shaped, each member having a front part at the facing of the structure and a pair of lower and upper rearward extensions interconnected by the front part. The rearward extensions of the support members will normally each be relatively short and connected to a respective stabilising element and for this purpose each extension may be formed with a vertical hole for receiving a connecting bolt. Thus it is particularly advantageous if each support member is formed as a strap or belt in which a suitable hole may be provided. The support members will thus be located at intervals across the structure corresponding to the lateral spacing of the stabilising elements; such intervals normally range from 0.5 to 2 m although for very high structures, the intervals may be less than 0.5 m. The length (height) of the support members will normally vary from 0.3 to 1 m. The support members may be formed of mild steel or half mild steel or equivalent and may optionally be galvanised.
The facing of the structure may be vertical or it may be at an angle to the vertical e.g. a slope of 4:1, 2:1 or 1:1 (vertical:horizontal). The stabilising elements will generally extend substantially horizontally in the earth mass, and therefore the rearward extensions of the support members will also be substantially horizontal, even if the facing is not vertical.
Preferably the mesh cover is also generally C-shaped and thus has relatively short lower and upper rearwardly projecting portions interconnected by and integral with a substantially flat front portion. The provision of two rear projections contributes to further stiffening of the cover against forward movement. In general, it is preferred that the cover comprises a mesh facing bent rearwards along its upper and lower edges to provide tow mesh stiffening projections. Thus the shape of the mesh cover will tend to correspond to that of the support members which support the cover. The length of mesh cover will normally be sufficient to span two, three or more support members and will generally be at least 2 m and no greater than 10 m to facilitate transportation.
The mesh cover will normally be formed of mesh elements or bars arranged at right angles to each other and may for example be steel wire mesh of the type conventionally used to reinforce concrete. The laterally extending mesh bars, which in practice will normally be horizontal, may be spaced at intervals ranging from 5 to 30 cm and preferably from 10 cm to 20 cm. The diameter of thebars will normally range from 5 mm to 15 mm and preferably from 6 mm to 10 mm. The mesh bars extending upwardly of the facing may be spaced at intervals generally a bit less than the lateral bars, for example at intervals ranging from 5 cm to 30 cm and preferably from 5 cm to 15 cm, e.g. 10 cm. Their diameter will usually be slightly less than the lateral bars, ranging from 4 mm to 12 mm and preferably from 5 mm to 8 mm. The steel used may be mild steel or half mild steel or equivalent and may optionally be galvanised.
It is desirable, although not essential, for the mesh cover to be arranged such that its lateral bars are on its outside face and its upwardly and rearwardly extending bars are on its inner face. Thus in the preferred C-shaped from of the cover the lateral bar or bars of the upper stiffening projection are located above the rearwardly projecting bars, and the lateral bar or bars of the lower stiffening projection are located below the rearwardly projecting bars. This arrangement can be particularly advantageous in securing the mesh cover to the support members, since the mesh cover may be arranged with the lateral bars of its front portion located behind or inwardly of a respective support member and the lateral bar or bars of its stiffening projection located outwardly of the rear extension of the support member. By threading the support member into the cover in this way, the rear extensions of the support members will each tend to lie in the lateral space between adjacent rearwardly projecting bars of the mesh cover i.e. in the same plane.
A porous sheet, such as a fine mesh, geotextile or, more preferably, a geogrid, may be placed behind the mesh cover of prevent fine soil particles from escaping past the facing. Such a sheet will also permit hydroseeding (or equivalent) of the facing. If crushed rock is used as the backfill then such a sheet will probably not be necessary.
The structure facing will usually consist of a plurality of rows arranged one above the other, each row comprising support members at lateral spacings across the structure and one or more mesh covers spanning between the support members. The support members of adjacent rows are preferably connected to each other, and in a preferred embodiment the rear extension of such support members are separated by a vertical gap in which is located the forward end of a stabilising element connected, e.g. by a vertical bolt, to both rear extension. If the lateral bars of the mesh cover stiffening projections of adjacent rows are outwardly arranged as discussed above, then these bars will ensure the presence of such a vertical gap between the support member rear extensions.
The facing will normally be sufficiently flexible to accommodate settlement of the stabilised earth both during and after construction. The preferred C-shape of the support members allows them to flex, and in a particularly preferred embodiment the front part of each support member is formed with an angular bend, preferably at the median line between the top and bottom of the member, which, when there is relative vertical movement between the top and bottom of the member, causes forward bowing of the cover to take place relatively uniformly. This arrangement can thus ensure that bending occurs in one horizontal line across the structure, avoiding uneven bulging or flexing of the support members which could make the facing unsightly.
The elongate stabilising elements may be any such elements used in earth stabilisation. In a preferred embodiment, the stabilising elements are steel strips as described in United Kingdom Patent No. 1563317.